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Air/gas in SWG with pump on low speed

Hi TFP,

I considered installing a Intelliflow variable speed pump to save on energy costs, but unfortunately I was given what Aussies call a 'bum steer' (look it up ) on the price so I went with a significantly cheaper variable speed pump that is available here in Sydney, the Hurlcon Viron P320. This pump has 3 speeds that can be set by the pool owner, but the factory set speeds equate to (according to manufacturer's data):

Low: 128 Lpm (28 gpm?), which runs at about 160W
Medium: 206 Lpm (45 gpm?), which runs at around 450W
High: 320 Lpm (70 gpm?), which runs at around 1100W

I figure I should be able to run a 8-10 hour low speed filtration cycle, which should provide 1 turnover. I don't have a flowmeter so I can't verify the above flow figures. Given my very ordinary plumbing setup I would be very surprised if I'm getting anything like the higher speed flow figures, but low speed should be pretty close?

Now to the topic of the post. When running the pump at lower speeds, not all the bubbles are being flushed out of the SWG and a larger bubble is forming in the top of the cell housing.

The SWG manual specifically states "WARNING: It is essential that pipe work and equipment do not allow gases generated from the cell to collect and build up", but I've read TFP posts where others are running with similar bubbles without worrying about it. Is running the SWG like this likely to damage the cell or cause other problems?

I rang the tech support for Hurlcon and they were pretty useless - their suggestion was to either turn down the SWG or turn up the speed of the pump. Thanks guys, I'd already worked that one out.

Re: Air/gas in SWG with pump on low speed

There are two things that can happen.

If the gas accumulates in the filter, one day it can blow up and you may find your filter couple of blocks away. It's pretty rare to happen, and usually means the chlorinator wasn't installed correctly.

If it accumulates within the cell the water level can get too low and the cell can overheat, melting the plastic housing and potentially exploding too.

Small bubbles aren't a concern, but if significant volume of the cell housing doesn't have water in it, and you can see the plates exposed, then i would look at increasing the flow

Re: Air/gas in SWG with pump on low speed

+1 for what Strannik said. Normally this is not an issue. Bubbles are normal and they don't generally accumulate enough to be a problem even when the pump is on low speed. However, if the bubbles are accumulating and filling the cell so the plates are exposed you need to do something.

Re: Air/gas in SWG with pump on low speed

Thanks guys, I've been playing around with speeds and chlorinator settings since first post. I've bumped up the low speed from 1375 to 1500 rpm, but even with the chlorinator set at the lowest settings (1/8 = around 4g/hr) the bubble slowly forms to the point where the cell plates are exposed. On Medium speed (2000rpm), the bubble forms if the chlorinator is set at anything higher than 2/8 or 3/8 full dose. For an 8 hour cycle I find that I need to run the chlorinator at around 4/8 full dose so I'm starting to get worried that I will not be able to use the benefits of the variable speed pump.

I tried running with the multi-port set to re-circulate and did not seem to have any problems on Medium speed (even at full dose), while on 1375rpm low speed I could get up to 1/2 dose before bubbles started to form. The pressure gauge did show a difference in each valve position when running low speed (filter = 20kPa/4psi, re-circulate = 15 kPa/3psi) which I assume is to be expected. Is there something in the filter that I should check?

As previously mentioned, my plumbing set-up is woeful, with way more pipe and bends than required. All lines are 1.5". I could re-plumb everything in 2" (all pipework is accessible) and set it up with way less bends. Unions on the filter, pool returns (no eye-balls) and skimmer would all still be 1.5". Do you think a re-plumb is likely to solve the problem or would I be wasting my time and money?

Re: Air/gas in SWG with pump on low speed

I should have also pointed out that all equipment is well below the water level, so there should be at least 1 metre of static head, plus plenty of head loss from about 10 metres of 40mm pipe and heaps of 90 deg bends. Do you still think the no eye-balls would be a problem?

I plan to experiment with some eye-balls anyway to see if they will improve skimming. The return pipes come through the wall at about a 45 deg angle. Are there eye-balls that would suit? All the ones I've seen have a 90 deg flange.

Re: Air/gas in SWG with pump on low speed

Thanks Mas, I agree re: the eyeballs. SWG works much better with multi-port set to re-circulate so it is obviously a flow issue. I don't really see increasing the rpm as an acceptable option though. I just spent $900 on this pump, which will be a complete waste of money if I can't run it at low speeds.

Below is a photo of my complete set-up - hope that helps. In case you can't make it out the suction line runs through 45-90-90-45-45-90-45-valve-90- immediately into pump. Discharge line runs through 90-90-filter. And no, I didn't install the pump. One of the warranty conditions for this pump is that it be installed by a 'trained installer'. I could have done a better job myself Unfortunately, the guy turned up about 90 minutes late and then didn't alter any of the factory set speeds. As he was so late I couldn't hang around until he was finished.

After the filter, the return line runs through 45-90-90-90-SWG-3 way valve-90-valve-90-45-45-90-towards returns. I figure I could turn the filter around and have the pump and SWG on the left hand side, which would allow a long straight suction line into the pump with no bends. Could then run 45-45 into the multi-port, then a series of 45s into the SWG, then 2 45s out of the SWG and back towards the returns. All of which would be 2" or bigger. Quite a lot of effort and expense (new valves) so I want to be pretty confident that it's going to make a difference. Any thoughts?

The plumb upside down option is an interesting suggestion. I can see why this would help, but as that contravenes the installation instructions I would have thought there is a reason not to do this?

Re: Air/gas in SWG with pump on low speed

You really won't get much more flow rate by changing the plumbing. The effect is minor.

I would contact the manufacture and find out why it cannot be installed upside down. It could be because the cell might collect debris. That really is a poor design and almost guarantees that gas will get trapped. A second option would be to lay it on it's side and make sure there is an easy path for the gas to escape (upwards). That should work almost as well and they might agree to that.

Re: Air/gas in SWG with pump on low speed

With respect, is this thread starting to drift off topic?

The off topic posts moved to the Deep End. JasonLion

Haven't tried the waterfall test yet ... I'll have to give that a go on the weekend. I've posted on another forum and found others wiith the same equipment who are not experiencing the problem. There must be a solution. No prizes for guessing what I'll be doing this weekend

Re: Air/gas in SWG with pump on low speed

More healthy debate

I haven't waited to see whether the bubble will cause the cell to shut down on 'no flow'. I realised that the cell shouldn't be operating with an expanding bubble in the housing, so on every occasion I have shut down the cell and/or run the pump on full speed to clear the bubble. I suppose I can try leaving it on until it cuts out, but I'm not sure I want to damage my cell or cause an explosion just to settle the debate

There does certainly appear to be something unique about my installation that is causing the problem, because I can only find one other similar report on the internet. As mentioned above, I have posted on a local forum (any forum in a storm) and there are others with similar equipment that are not experiencing this issue.

I like the idea of the waterfall test and will give it a try. Depending on how risk averse I feel on the day I might even run the cell until it cuts out. I intend to check out the internals of all the valves that are installed - in particular the 3 way valve. I also intend to open the filter and inspect to see if there is anything untoward.

Re: Air/gas in SWG with pump on low speed

Thanks Jason - I was wondering if someone was going to step in.

I did a bit more playing and felt brave enough to leave the pump on low speed a bit longer. Here's some photos of what happened at low speed (supposedly 128 Lpm/28gpm) and chlorinator on half (15g/hr - don't ask me to convert that to ounces):

After 10 minutes:

After 30 minutes - still not tripping on No Flow, but the Low Salt light is on:

The main problem with the design is the orange bar that runs across the top front of the cell. This creates a point of turbulence where bubbles start to form in the eddy downstream of it. It also acts as a barrier for the bubble that forms upstream of it.

Re: Air/gas in SWG with pump on low speed

That's a pretty significant amount of gas in there after only 10 minutes.
28 gpm isn't very low flow not nearly low enough to be causing that much gas to be entrained.
I wonder if part of your problem is because the unit is below the waterline?

Have you tried putting the multiport on recirc and seeing if the air space is lessened or goes away completely?

There's not some insert or diverter missing or damaged on the inlet side of the cell is there?

Re: Air/gas in SWG with pump on low speed

Pressure is relative and should not make a difference so the height of the cell or the fact that it is below water level has little impact on the problem. It is all about flow rate.

The biggest problem is with the design of the cell had having the ports at the bottom of the cell. This makes the gas much easier to trap in the cell at lower flow rates. Axial cells don't have this issue because the gas is much easier to purge out of the cell. However, even with the axial cells, the gas can still get trapped in another parts of the plumbing at low rates. But I would be much more concerned about the gas getting trapped in the cell since exposed plates could potentially ignite the gas.

In my own system, I have a high spot right before my last return so the gas tends to collect there on low speed. Occasionally, there is a large bubble of gas that burps out of the return. I once collected the gas and ignited it to see how volatile it was and believe me, you do not want the gas in your cell to ignite. It is pretty violent.

I think your only hope is get more flow rate either with a higher RPM or lower return head loss with the waterfall on. I suspect though you may end up having to run on higher speeds.

Re: Air/gas in SWG with pump on low speed

Have you tried putting the multiport on recirc and seeing if the air space is lessened or goes away completely?

Yes, as mentioned in one of my earlier posts, running on re-circulate significantly reduces the problem

Originally Posted by Bama Rambler

There's not some insert or diverter missing or damaged on the inlet side of the cell is there?

No

Originally Posted by Bama Rambler

I wonder if part of your problem is because the unit is below the waterline?

I've since found others that don't have the problem (both above and below water line installations) and at least one that does (above water line installation). I agree with Mas - in each case the pressure is relative and above/below waterline should be irrelevant.

Originally Posted by mas985

Pressure is relative and should not make a difference so the height of the cell or the fact that it is below water level has little impact on the problem. It is all about flow rate.

Agree. I have just been comparing photos of another installation (same model cell and pump) that does not have the problem Vs mine. I noticed in the other installation that a) the cell housing is installed so as to get a straight run of pipe on the inlet, and b) the cell housing is tilted slightly (rounded end up). Both of which may help, but I think I read somewhere that the cell should ideally be installed at just below the level of the multi-port return. Is there any disadvantage to installing it higher than the multi-port?

Re: Air/gas in SWG with pump on low speed

I doubt that height makes real difference, though I can think of some minor issues. Heights that require longer pipes, or worse more bends in the pipe, could make things just slightly worse since the flow rate will go down just slightly due to the longer, more flow resistant, plumbing. Second, you never want to position it in a way that allows gas to run backwards towards the filter (even when the pump is off). I believe the normal install precludes that from ever happening, but someone mentioned mounting it sideways or upside down, and that could easily result in gas being able to run back towards the filter when the pump was off (or just maybe even when the pump was on, depending on setup).

Re: Air/gas in SWG with pump on low speed

Originally Posted by OzPool

Is there any disadvantage to installing it higher than the multi-port?

Reducing the downward path that the bubbles need to travel should help to purge them from the cell. This is a theory but some of the bubbles may be going out the port but because the pipe is so long, can't make it to the bend and so collect at some point and travel back upwards to the cell.

If you can make the downward pipe after the cell as short as possible and go horizontal directly into the return valve, that might help move the bubbles away from from the cell. However, even you put a 90 on the output port of the cell next to the coupler, the bubbles still need to make that bend which will still require at least a good amount of flow. But it is probably worth a try if nothing else works.